Deploying .msi applications w/o product key or passing it to first run

I couldn't find anything specific on this subject so I'll give this a shot.

Because of licensing (we have multiple volume keys depending on vendor used), I am trying to figure out the best (read easiest, as one universal package w/o key) way to package/ deploy MS .msi applications that require a product key during the install w/o specifying the key during the install and requiring the end user to enter the key?